Method of effecting magnetic deformation of a workpiece



Feb. 23, 1965 A. C. DUCATI METHOD OF EFFECTING MAGNETIC DEFORMATION OF A WORKPIECE Original Filed Dec. 15, 1959 3 Sheets-Sheet l a? L FIG. la; m

VII/ll/ll/lVl/I/ INVENTOR.

ADRIANO C. DUCATI MKM ATTORNEY.

A. C. DUCATI Feb. 23, 1965 METHOD OF EFFECTING MAGNETIC DEFORMATION OF A WORKPIECE 3 Sheets-Sheet 3 Original Filed Dec. 15, 1959 FIG.5.

FIG. 6.

V4600 Pad/P FIG. 8.

INVENTOR.

ADRIANO C. DUCATI W ATTORNEY.

United States Patent 9 Claims. (Cl. 219-149) This invention relates to a method of working, forming or deforming a workpiece such as a sheet or tube of metal. The application is a continuation of co-pending application Serial No. 859,765, filed December 15, 1959, now abandoned, for Method of Etfecting Magnetic Deformation of a Workpiece.

The object of the present invention is to provide a method of forming, flattening, coining and otherwise working metal sheets, tubes and the like in a highly simple manner wh ch is readily susceptible of mass production, and wh ch is characterized by the utilization of strong magnetrc fields of short duration.

Another object of the invention is to provide a method of achieving superior results including the precise duplication of markings on a pattern, the formation of unusual shapes with only one mold or with no molds, the simultaneous molding of two sheets in the absence of a male mold, etc.

These and other objects and advantages of the invention will be more fully set forth in the following specification and claims, considered in connection with the attached drawings to which they relate.

In the drawings:

FIGURE 1 is a schematic vertical sectional'view illustrating mold means and electric circuit means employed to perform methods relating to the flattening, thinning, working and marking of a workpiece;

FIGURE 1a corresponds to FIGURE 1 but illustrates a mold construction adapted to result in punching of a workpiece;

FIGURE lb corresponds to FIGURE la but illustrates the workpiece configuration which results when less electric power is applied, so that no punching or shearing results;

FIGURE 2 illustrates electric circuit and mold means employed to effect simutaneous forming of two flat sheets of metal into the upper and lower sections of a tank or the like;

FIGURE 2a illustrates the vessel which results after welding of such upper and lower vessel sections together;

FIGURE 3 is a schematic longitudinal sectional view illustrating apparatus for forming male threads on a section of tubing;

FIGURE 4 is a vertical central sectional view illustrating apparatus characterized by radial flow of current and incorporating mold means to effect forming of a vehicle wheel or the like;

FIGURE 5 is a schematic sectional view illustrating electric circuit means for effecting parallel flow of current through adjacent conductors to create attractive forces therebetween, as distinguished from the anti-parallel current flow and consequent repulsive forces utilized in the methods illustrated in the previous figures;

FIGURE 6 is a schematic view illustrating the use of parallel currents, one flowing through the workpiece and one through an electrically-conductive mold, to provide predetermined deformation or working of the workpiece;

FIGURE 7 is a schematic longitudinal sectional view illustrating the use of parallel currents to effect threading of a metal tube with female threads;

FIGURE 8 is a schematic sectional view illustrating radial current flow with parallel currents;

1 'ice FIGURE 9 is a view corresponding to FIGURE 8 but illustrating means for effecting cooling of the workpiece.

Before proceeding to a detailed description of the embodiments shown in the drawings, there will be given a brief summary of various forms of the invention. In accordance with one of its aspects, the present invention comprises a method of magnetically forming a workpiece by relating to the natural resonant or ringing frequency of such workpiece the time period during which a highcurrent pulse of electricity is passed therethrough. In another of its aspects, the invention relates to a method of punching a hole in a sheet of electrically-conductive metal by passing current pulses adjacent such metal and in anti-parallel relationship, the pulses being sufficiently large to cause shearing of a portion of the sheet so that the hole results. Relative to another major aspect to the invention, predetermined portions of electrically-conductive workpieces are restrained in various ways, and large electric currents are caused to flow through and adjacent such workpieces in such manner as to generate strong magnetic fields resulting in magnetic forming thereof.

Referring to FIGURE 1 of the drawings, the workpiece is indicated at 10 and may comprise a sheet of copper, stainless steel, or various other electrical conductors. Workpiece 10 is disposed over a correspondingly shaped but normally substantially thicker block 11 of a highlyconductive metal such as copper. One edge of block 11 is in low-resistance surface contact with workpiece 10 at the interface 12. The remaining portion of the block 11, that is to say all portions of the block excepting at the interface 12, is recessed to receive a thin sheet 13 of insulating material, it being understood that the thickness of the insulation is exaggerated in the drawing. The insulation may comprise a thin sheet of Mylar.

A block 14 of insulating material, of an incompressible nature, is mounted over the upper surface of workpiece 10. The illustrated insulating block 14 has a recess 15 in its underside adapted to receive a solid mold 16 which is in surface engagement-with the workpiece. As will be indicated below, for certain operations the recess 15 and mold 16 may be eliminated so that the entire undersurface of the insulating block 14 is in flatwise engagement with the workpiece 10. Back-up means 17 are mounted against the upper surface of insulating block 14 and against the lower surface of electrical-conductor block 11 to prevent these elements from moving further apart as a result of magnetic forces.

A suitable source 18 of high-current pulses is connected through leads or buss bars 19 and 20 to the workpiece 10 and to conductor block 11. The electrical connections between the leads 19 and 20 and elements 10 and 11 are remote from interface 12, and are of a type providing a minimum of contact resistance. Furthermore, such electrical connections extend for substantial distances perpendicular to the plane of the drawing. A switch 21 is interposed in one of the leads 19 and 20.

The pulse source 18 may comprise a bank of capacitors adapted to be charged from a suitable source of voltage, not shown, and then discharged through the elements 10 and 11 upon closing of the switch 21. The switch 21 may comprise, for example, a spark gap between two parallel conductor bars, so that current fiow will occur when the atmosphere between the bars 1s ionized as by a suitable triggering electrode.

The method will first be described with referen to reproducing in workpiece 10 the markings, embossments, etc., present on the lower surface of the mold or pattern 16 disposed in recess 15. As previously indicated, the thickness of the mold 16 is substantially the same as the depth of the recess 15, so that upward movement of the workpiece 10 will immediately bring it into close pressure contact with the mold. Pulse source 18 is then suitably charged, and switch 21 is closed. Assuming that the polarities are as indicated, current flows from source 18 through lead 19 to workpiece 10, then through the interface 12 to the conductive block 11, then through lead 20 and switch 21 back to the pulse source 18.

Since the currents thus flowing through workpiece and block 11 are anti-parallel, and since the opposed surfaces of these members are insulated from each other but close together, strong and uniform magnetic forces are created in each molecule of the workpiece 10 to force it upwardly against the mold 16. Such forces cause the upper surface of the workpiece 10 to conform exactly to the shape of the lower surface of mold 16. Where the mold 16 is substantially embossed, the entire adjacent portion of workpiece it} may bend and deform to reproduce the embossment.

Successful operations have shown that this method produces a highly faithful and precise reproduction of very minute markings, for example tool marks. Where the lower surface of mold 16 is provided with slightlyraised printing, the upper surface of workpiece 10 will be correspondingly depressed to create an etched appearance. The method is therefore highly useful in reproducing printing plates and the like.

As a specific example of the above method, the pulse source 16 may be a bank of capacitors having 100 microfarad capacitance, charged to about 10,000 volts, and capable of delivering 5,000 joules. The workpiece 10 may be a sheet of copper having a thickness of 0.012 inch, and the mold 16 may be a metal disc /2 inch in diameter and having an embossed lower surface. The area of sheet 10 may be on the order of one square inch. With such factors, closing of switch 21 causes current flow of several hundred thousand amperes through the above-described circuit, for a time period of several microseconds. As stated heretofore, the copper sheet 10 is deformed into a highly faithful and accurate reproduction of the embossment on the lower mold surface.

Let it next be assumed that the recess 15 and mold 16 are eliminated, so that the entire lower surface of insulating member 14 is plane. With such an arrangement, discharge of pulse source 18 causes the workpiece 10 to be flattened against the undersurface of member 14. The method is, therefore, highly useful in the flattening of workpieces to a high degree of accuracy. Furthermore, the method is operative to cause the workpiece 10 to become thinner than previously, either in spots or over a substantial area. By repeatedly discharging the pulse source 18 (or a bank of such sources) through the abovedescribed circuit, the workpiece 10 may be worked, as with a hammer, to provide changes in the characteristics of the metal. As will be set forth below, the flow of current through the workpiece 10 effects predetermined heating thereof to aid in the forming or working process.

Referring next to FIGURE 1a, the method is identical to that described with reference to FIGURE 1 except that the insulating mold 14a is formed with a hole 23 which may be round, for example. The upper back-up block 17 is correspondingly open to permit discharge of metal out the hole 23, and also to permit escape of air. When a large amount of power is employed, closing of switch 21 operates to effect instantaneous shearing or punching of a hole 24 in the workpiece 10, the shape of the hole corresponding to the shape of the hole 23 in the mold or die 14a. Especially where the workpiece 10 is thin, the metal which was removed to form the hole 24 does not retain a disc shape but instead becomes highly crinkled as indicated at 26. The reason for such crinkling of the disc is not understood.

Referring next to FIGURE 1b, the method is identical to that shown and described with reference to FIGURE 1a except that an insuflicient amount of power is employed to effect shearing or hole-punching. Where the amount of power is just below that which is adapted to form a hole (as described with reference to FIGURE 1a), a bulge 27 is formed having a central upwardlyextending protuberance 28 at its center. Protuberance 28 is characteristic of the magnetic forming process, since no comparable protuberance results when mechanical forming means are employed. At even lower powers, the bulge is lower and there is little or no protuberance.

It is a feature of the invention that various shapes may be free-formed magnetically, without the use of either male or female molds, by varying factors such as current magnitude, etc. Thus, assuming that the mold opening 23 is relatively large, two or more sets of pulse sources 18 and corresponding leads may be connected to effect flow of different quantities of current through selected portions of the region of workpiece 10 which is registered with the opening 23. Such different quantities of current result in variation of the shape of the bulge 27. Accord ingly, the shape of the bulge 27 may be controlled by empirically adjusting relative current magnitudes, flow directions, and the like.

Referring next to FIGURE 2, an apparatus is illustrated for elfecting magnetic forming of two sheets of metal simultaneously. The apparatus comprises upper and lower insulating molds 31 having recesses 32 in their adjacent surfaces. The walls of the recesses 32 are illustrated as being dome-shaped, but it is to be understood that the walls may have various other shapes. Further more, the molds 31 may have openings therein to permit free-forming of various shapes as described with reference to FIGURE 1b. Vacuum pumps 33 are connected to the recesses 32 by means of conduits 34, so that there will be no compressed-air effects when the metal sheets are projected toward the walls of the recesses 32. It is to be understood that corresponding vacuum means may be employed in connection with other embodiments, such as the embodiment of FIGURE 1.

Two corresponding electrically-conductive metal sheets 36 and 37, having a sheet of insulation 38 therebctween, are mounted parallel and adjacent to each other between the molds 31. The sheets 36 and 37 completely cover the recesses 32, the edge portions of the sheets being clamped between the molds 31 around the recesses. It is to be understood that suitable back-up means, not shown, are provided to prevent the molds 31 from moving away from each other.

The electric circuit means illustrated in FIGURE 2 comprise a pulse source 39, a switch 41 and a variable inductor 42 connected in series with each other across the metal sheets 36 and 37. The source 39 and switch 41 may correspond to the elements indicated at 18 and 21 in FIGURE 1, whereas the inductor 42 may be of any suitable construction adapted to handle large currents. The leads or buss bars 43 and 44 which extend from source 39 to sheets 36 and 37 are connected, by low-resistance connections, to such sheets along the full lengths of adjacent edges thereof. The portions of the sheets 36 and 37 remote from such connections are electrically connected to each other as by the lead 46, the latter also extending for the full lengths of adjacent edges of sheets 36 and 37. Thus, upon closing of the switch 41 to effect current flow from pulse source 39 to the sheets 36 and 37, the currents will flow in anti-parallel relationship through such sheets and through connecting lead 46.

The anti-parallel currents flowing instantaneously through sheets 36 and 37 produce large magnetic forces which propel the sheets apart until they engage and conform to the dome-like walls of recesses 32. In freeform operations performed with this method, the surprising result has been noted that the distance each sheet is forced away from the central plane (through insulator 33) is substantially the same where two sheets are formed simultaneously as it is where only one sheet is formed and the other is a fixed electrically-conductive element as in FIGURE 16.

According to one feature of the method, the current flow through sheets 36 and 37 is so regulated that the sheets become resistance-heated to temperatures only slightly below their melting point. This is accomplished by performing a number of test runs and progressively increasing the amount of applied power until one or both of the sheets melt. The power is then reduced by a relatively small amount, so that it is known that the sheets are heated almost to their melting point. By this method, it is possible to form metals which are difficult or impossible to form by ordinary means.

In accordance with another feature of the method, the duration of the current pulse passed through the sheets 36 and 37 is caused to be at least as long as one fourth of the time period required for each full cycle of the natural resonant or ringing frequency of each sheet 36 and 37. Thus, if each sheet 36 and 37 has a natural resonant frequency of 1000 cycles per second, the variable inductor 42 is so adjusted that the duration of the current pulse resulting from closing of switch 41 is at least $4 of a second (0.00025 second). The enormous magnetic force resulting from discharge of the pulse source thus operates, for at least the time period required for one-quarter cycle of the resonant frequency of the sheets of metal, to project the sheets toward the mold surfaces with great efficiency.

Referring next to FIGURE 2a, upper and lower shell sections 47 and 48 are shown, having been formed from sheets 36 and 37 as described with reference to FIGURE 2. To make a complete tank or the like, it is merely necessary to trim the portions of sheets 36 and 37 around the peripheral portions of the recesses 32, and then make the peripheral weld indicated at 49. It is pointed out that the edge portions of the molds 31 prevent the peripheral portions of sheets 36 and 37 from flying apart as a result of the magnetic pressures.

Proceeding next to a description of FIGURE 3, an

apparatus is illustrated for instantaneously forming external threads on a metal tube or workpiece 51. Such apparatus comprises an internally-threaded mold 52 disposed closely around the unthreaded tube 51, a tubular insulating member 53 disposed within the tube 51 and engaged with the interior wall thereof, and an electrically-conductive tube 54 disposed closely within the insulating member 53. The tube 54 may be filled, as with -an insulator 56, to insure against collapse thereof. An

electrical conductor plug 57 is provided at one end of the assembly to electrically connect the adjacent ends of workpiece 51 and conductor 54. The leads 43 and 44 described with reference to FIGURE 2 are connected, respectively, to adjacent ends of conductor 54 and workpiece 51.

In performing the method with the apparatus shown in FIGURE 3, discharge of pulse source 39 upon closing of switch 41 causes a large current pulse to flow through lead 44, workpiece 51, conductor plug 57, and back through conductor 54 to the lead 43. The resulting magnetic force operates to force tube 51 radially outwardly against the internal threads on mold 52. The entire tube 51 is thus provided with male threads in a fraction of highly-conductive metal block 60 which is disc shaped and has a central protuberance 61. Protuberance 61 projects upwardly through a central opening in insulator 59 and is in fiatwise engagement with the center portion of disc 58 at the lower surface thereof. A block 62 of .insulating material is fixedly secured beneath conductor block 60, and an insulating mold 63 is fixedly secured above the disc 58. Mold 63 is solid except for an annular recess 64 which is coaxial with the protuberance 61. The center portion 66 of the mold 63, radially-inwardly of the recess 64, is in flatwise engagement with the upper surface of disc 58 above protuberance 61. Mold center 66, and the peripheral portion of the mold around recess 64, operate to maintain the adjacent portions of disc 58 in engagement with protuberance 61 and insulator 59.

Upper and lower electrically-conductive rings 67 and 68 are mounted concentrically around the workpiece 58 and metal disc 60, respectively, in continuous electrical contact therewith. The leads 43 and 44, which were described in connection with FIGURE 2, are respectively connected to the rings 68 and 67 to effect feeding of current to the peripheral portions of block 60 and metal disc 58. A vacuum pump 69 is connected through conduits 70 to the annular recess 64 in order to effect evacuation thereof.

Upon closing of switch 41 to discharge the pulse source 39, current flows radially inwardly from ring 67 to the entire peripheral portion of the disc or workpiece 58 and thence to the center of such workpiece. The curent then flows downwardly through protuberance 61 and radially outwardly through block 60 to ring 68. With the described anti-parallel radial current flow, the current density and the magnetic force are much greater adjacent the center of workpiece 58 than at the periphery thereof. It is pointed out that the upper wall of recess 64 is spaced farther from workpiece 58 near the center of the workpiece than at the periphery thereof. However, because of the described variation of the magnetic force, the workpiece is effectively projected against the wall of the recess 64 at all portions thereof. During such magnetic forming operation, the workpiece 58 bends and may also stretch to a certain degree. The described method may be employed in manufacturing a vehicle wheel, for example.

Proceeding next to a description of FIGURE 5, an embodiment is illustrated in which the flow of current through adjacent conductors is parallel as distinguished from antiparallel, the latter type of current flow having been employed in the previous embodiments. Two electricallyconductive rectangular sheets or plates 71 and 72 are disposed in flatwise engagement with each other, and connectors 73 are disposed in electrical contact with the end edges of both sheets. A suitable pulse source 74 is connected to one of the end members 73, and a suitable switch 75 is connected to the other, the elements 74 and 75 being in series with each other. These elements may correspond to the pulse source 18 and switch 21 previously described.

In performing the method with the embodiment of FIGURE 5, closing of switch 75 effects parallel current flow through all portions of the plates 71 and 72. This creates a strong magnetic force tending to force the plates together, as indicated by the vertical arrows. The magnetic force operates to flatten, thin, work, mold, etc.

Referring next to FIGURE 6, an electrically-conductive rectangular workpiece 77 is disposed adjacent and over an electrically conductive mold 78, the center of such mold being suitably embossed or otherwise shaped as indicated at 79. Electrically-conductive end members 83 and 84 are connected, respectively, to pulse source 74 and switch 75 of FIGURE 5, so that closing of the switch effects parallel current fiow as indicated by the arrows in FIGURE 6. An endless groove 80 is provided in the upper surface of mold 78, around the embossed portion 79, and is connected to a vacuum pump 82. Suitable seal means, not shown, are provided to prevent entrance of air into groove 80.

In performing the method with the apparatus of FIG- URE 6, vacuum pump 82 is first operated to evacuate the space between workpiece 77 and mold 78. Thereafter, pulse source 74 is discharged through members 77 and 78,

resulting in magnetic forcing of workpiece 77 against the mold. The lower surface of the workpiece is thus caused to conform to the embossed mold portion 79.

Referring next to FIGURE 7, an electrically-conductive tubular workpiece 86 is mounted closely around an electrically-conductive cylindrical mandrel 87 having male threads 88 which engage the interior surface of the workpiece. A solenoid 89 is mounted coaxially around members 86 and 87, being connected across switch 75 and pulse source 74 of FIGURE 5. Discharge of the pulse source effects parallel flow of induced currents through the tube 86 and mandrel 87 at right angles to the magnetic field created by the solenoid. The magnetic force created by the induced currents causes reduction in the diameter of the workpiece 86 until the interior surface thereof is threaded with female threads corresponding to threads 83. This method is particularly useful in forming fine threads, which are difficult to machine, but it may also be employed for forming coarser threads. After the threading operation, the workpiece 36 is unscrewed from the mandrel 87.

FIGURE 8 shows an embodiment in which the parallel current fiow is radial as distinguished from longitudinal. Two metal discs 92 and 93 are disposed in fiatwise engagement with each other, and an electrically-conductive ring 94 is mounted around the peripheries of both discs in continuous electrical contact therewith. Two terminal blocks are disposed in electrical contact with the centers of the discs, being suitably connected to the switch '75 of FIGURE 5. When the ring 94 is connected to pulse source 74 of FIGURE 5, and the switch 75 is closed, parallel currents flow radially-inwardly from ring 94 to blocks 96 to generate magnetic forces which squeeze the plates 92 and 93 together. Such forces are much stronger at the center portions of the plates than at the peripheries thereof, due to the higher current density, so that extremely forceful and accurate forming or working operations may be performed at the center. The described apparatus and method make it possible to employ extremely high current flows with a minimum of contact resistance and losses, there being a large amount of surface area between ring 94 and the peripheral surfaces of the discs 92 and 93.

FIGURE 9 illustrates an embodiment which is identical to the embodiment of FIGURE 8, except that annular cooling members 7 are mounted around each block 96 in surface engagement therewith and with the exterior surfaces of workpieces 92 and 93. Water or other suitable coolant is passed through chambers in the elements 97, by means of conduits 98, to effect cooling of the workpieces. Such cooling means make it possible to employ extremely large currents without melting the workpieces. It is to be understood that the connector elements 94 and 96 may also be provided with cooling passages or chambers. It is also to be understood that suitable mold means may be disposed between the center portions of the elements 92 and 93, for example to provide impressions on the adjacent surfaces of such elements upon discharge of current therethrough. Elements 97 may be formed of insulating material.

The appended claims should not be interpreted as being limited with regard to the number of currents, or electric circuits, which are employed. Thus, for example, when first and second currents are recited, these may actually be the same current, but flowing in different parts of a single electric circuit.

The term anti-parallel, as employed in the appended claims, denotes current flow along parallel paths but in opposite directions. Thus, for example, if two adjacent ends of a pair of parallel wires are electrically connected to each other, and the remaining adjacent ends of such wires are respectively connected to the terminals of a battery, the resulting currents flowing in the respective wires are anti-parallel relative to each other.

Various embodiments of the present invention, in addition to what has been illustrated and described in detail may be employed without departing from the scope of the accompanying claims.

I claim:

1. A method of magnetically forming a workpiece having a predetermined natural resonant or ringing frequency, said natural resonant frequency being such that each full cycle requires a predetermined period of time for its completion, which method comprises passing a pulse of electric current through said workpiece for a period of time at least as long as one-quarter said predetermined period of time, and simultaneously passing a pulse of electric current adjacent and parallel to said first-mentioned pulse and sufficiently large to create a strong magnetic field effecting forming of said workpiece.

2. In a method of magnetic forming, the steps of providing a generally disc-shaped electrically-conductive workpiece, providing an electrically-conductive element parallel to and adjacent at least one surface of said workpiece, effecting flow of a large electric current radially through said workpiece and parallel to said electrically-conductive element, effecting flow of a large electric current through said electrically-conductive element parallel to said radial flow through said workpiece to create a strong magnetic field, said currents being sufficiently large that said field effects magnetic forming of said workpiece, and restraining at least portions of said workpiece in a predetermined manner.

3. A method of punching a hole in a sheet of electrically-conductive metal, which comprises providing a back-up element having an opening therein, disposing a sheet of metal adjacent said back-up element and over said opening, effecting flow of a large pulse of electric current through said sheet and parallel to the surfaces thereof, and simultaneously effecting a flow of a large pulse of electric current in anti-parallel relationship to said first-mentioned pulse and on the opposite side thereof from said back-up element, said pulses being sufficiently large to effect generation of a magnetic field sufiiciently strong to cause shearing of said sheet at the edge of said opening.

4. A method of effecting simultaneous forming of two sheets of metal, comprising disposing said sheets closely parallel and adjacent to each other, restraining the peripheral portions of said sheets against substantial movement in directions perpendicular to said sheets while permitting substantial movement of the central portions of said sheets in said perpendicular directions, and effecting simultaneous flow of large electric currents through said sheets in planes parallel to the planes of said sheets and with the current in one of said sheets in anti-parallel relationship relative to the current in the other to generate strong repulsive magnetic fields, said currents being sufiiciently large that said fields are sufficiently strong to effect movement of the central portions of said sheets in opposite directions for forming thereof.

5. The invention as claimed in claim 4, in which said method comprises causing said currents to be sufficiently strong to effect resistance-heating of said sheets to temperatures near but below the melting points of said sheets.

6. The invention as claimed in claim 4, in which said method includes the steps of determining the natural ringing or resonant frequency of at least one of said sheets, and causing said currents to continue for a period of time at least as long as one-quarter of the time required for each full cycle of said natural frequency.

7. The invention as claimed in claim 4, in which said method includes the step of providing mold surfaces spaced from said central portions of said sheets on opposite sides thereof, and evacuating the spaces between 9 said sheets and said mold surfaces prior to fiow of said currents.

8. The invention as claimed in claim 4, in which said method comprises the subsequent step of sealingly connecting the peripheral portions of the formed sheets to provide a completed vessel.

9. A method of effecting forming of a generally discshaped electrically-conductive sheet, which comprises restraining predeterrnined portions of said sheet against substantial movement in a direction perpendicular to said sheet while permitting other portions of said sheet to move in said direction, effecting radial flow of a strong electric current pulse through said sheet between the periphery and the center portion thereof, and efiecting 10 flow of a strong electric current pulse in anti-parallel relationship relative to said first mentioned pulse and in such relation to said sheet that said other portions of said sheet are impelled magnetically in said direction.

References Cited by the Examiner UNITED STATES PATENTS 1/46 Franz ..153--93 3/61 Harvey et al. 219-153 

2. IN A METHOD OF MAGNETIC FORMING, THE STEPS OF PROVIDING A GENERALLY DISC-SHAPED ELECTRICALLY-CONDUCTIVE WORKPIECE, PROVIDING AN ELECTRICALLY-CONDUCTIVE ELEMENT PARALLEL TO AND ADJACENT AT LEAST ONE SURFACE OF SAID WORKPIECE, EFFECTING FLOW OF A LARGE ELECTRIC CURRENT RADIALLY THROUGH SAID WORKPIECE AND PARALLEL TO SAID ELECTRICALLY-CONDUCTIVE ELEMENT, EFFECTING FLOW OF A LARGE ELECTRIC CURRENT THROUGH SAID ELECTRICALLY-CONDUCTIVE ELEMENT PARALLEL TO SAID RADIAL FLOW THROUGH SAID WORKPIECE TO CREATE A STRONG MAGNETIC FIELD, SAID CURRENTS BEING SUFFICIENTLY LARGE THAT SAID FIELD EFFECTS MAGNETIC FORMING OF SAID WORKPIECE, AND RESTRAINING AT LEAST PORTIONS OF SAID WORKPIECE IN A PREDETERMINED MANNER. 